herdity

Dominant

A trait that is expressed over another trait.

Recessive

A trait that is not expressed, unless there are two alleles of the same kind.

Homozygous

Two alleles of the same kind (TT or tt), for the same gene.

Heterozygous

Two alleles for different traits (Tt), but of the same gene.

Carrier

Often associated with a disorder, this term is used to describe an individual that is heterozygous for a trait. This acknowledges that the individual can pass the trait to their offspring, but that the person does not express it.

Allele

A version of a gene, typically represented by one letter (A or a).

Probability

Chance of an outcome occurring.

Pedigree

A visual representing the phenotypes of a family.

Phenotype

The physical trait that an individual has (ex. tall).

Genotype

The alleles that an individual has for a particular gene (ex. Tt).

Monohybrid Cross

A genetic cross to determine the probability of the offspring inheriting one gene.

Dihybrid Cross

A genetic cross to determine the probability of the offspring inheriting two genes.

Sex-linked trait

A trait that is found on a sex chromosome (Either X or Y).

Codominance

Form of inheritance in which both alleles are dominant and expressed. (a black rooster and a white chicken mate to make a chick that is black and white).

Incomplete dominance

Form of inheritance in which neither allele is dominant and so a blend is expressed. (a red flower and white flower mate to make a pink flower).

Multiple Alleles

Form of inheritance where many versions of an allele exists. (ex. Blood Typing - two versions of the dominant I gene)

Epistasis

Form of gene expression, where one gene controls or modifies the expression of another gene (ex. coat color in Labrador retrievers - black, brown, or yellow)

Polygenic Traits

Form of gene expression, where the number of dominant alleles from a series of genes control the phenotype expression. (ex. skin color - AABbcc, AaBbCc, and AabbCC have the same expression)

Law of Dominance

Mendel's Law that claims when there are two versions of a gene present within an organism, one version will be expressed over the other.

Law of Independent Assortment

Mendel's Law that claims each allele separates independently when creating gametes.

Law of Segregation

Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete